FIELD OF THE INVENTION
The present invention relates generally to medication infusion pumps, particularly of the type adapted for implantation directly into the body of a patient and for programmed operation to deliver medication to the patient, and more particularly to a medication infusion pump having an improved valve seat designed to minimize or prevent accumulation of medication deposits thereon.
Medication infusion pumps are generally known in the art for use in delivering a selected medication to a patient in a scheduled or preprogrammed manner. In recent years, infusion pumps have been developed in compact form and adapted for direct implantation into the body of a patient, to deliver a specific medication such as insulin to the patient in discrete doses over an extended time period. An implantable infusion pump of this general type includes an internal medication chamber for receiving and storing a supply of the selected medication in liquid form, in combination with a miniature pump mechanism and associated programmable control means for operating the pump mechanism to deliver discrete doses of the medication from the internal storage chamber and through a catheter to the patient. For one illustrative example of an implantable medication infusion pump of this general type, see U.S. Pat. No. 4,573,994, to Fischell et al.
The internal pump mechanism typically comprises an electromagnetically driven pulsatile pump having a solenoid operated piston mounted for reciprocation within a cylinder to draw medication from the internal storage chamber, and to deliver such medication through the catheter to the patient. The pulsatile piston operates in conjunction with an inlet check valve having a spring-loaded valve member movable between open and closed positions with respect to an annular valve seat. The valve member and valve seat are normally constructed from biocompatable and relatively inert materials, such as a movable valve disk of a silicone elastomer material and a rigid annular valve seat defined at the end of a ferrule formed of a titanium or titanium alloy. For examples of pulsatile pump mechanisms used in implantable infusion pumps, see U.S. Pat. No. 4,568,250, to Falk et al.; U.S. Pat. No. 4,569,641, to Falk et al.; U.S. Pat. No. 4,636,150, to Falk et al.; and U.S. Pat. No. 4,714,234, to Falk et al.
Despite the relatively inert characteristics of the traditional valve member and valve seat materials, medication deposits having a particle-like structure are known to accumulate over a period of time in the vicinity of the valve seat. The formation of such medication deposits is believed to be attributable to shear denaturation and/or precipitation of pharmaceutical components in response to relatively high mechanical stresses applied to the medication in the immediate vicinity of the valve seat, as the valve member moves between the open and closed positions. Such deposits are especially likely when relatively complex medications having a relatively large molecular structure are used, such as protein based pharmaceuticals including insulin and others.
Moreover, protein and other organic constituents present in such pharmaceuticals exhibit a tendency to adhere to the surface of titanium metal components, resulting in an accumulation of proteinaceous deposits at the valve seat. This presence of medication deposits is undesirable and may over time result in valve leakage, typically in the form of undesirable back-flow of body fluids into the interior of the implanted infusion pump.
There exists, therefore, a need for improvements in pump mechanisms for use in medication infusion pumps, wherein the pump mechanism includes an internal check valve designed to minimize or eliminate accumulation of medication deposits in the vicinity of a valve seat. It is accordingly the objective of the present invention to fulfill these needs and to provide further related advantages.